While I'm usually in great favor of all internationalization improvements, I'd prefer us not to adopt this change.

A decrease in font-size by 5-10% may seem trivial, but it would set the widget title at the same visual hierarchy level as an image caption or a blockquote. It would also reduce the size difference between heading and regular text by ~25%!

We can't account for all translations for all default widget titles in all sidebar widths. It would be great if we could not start attempting.